Package org.apache.lucene.store

Class Directory

java.lang.Object
org.apache.lucene.store.Directory
All Implemented Interfaces:
Closeable, AutoCloseable
Direct Known Subclasses:
BaseDirectory, FilterDirectory, NRTCachingDirectory
public abstract class Directory extends Object implements Closeable
A Directory is a flat list of files. Files may be written once, when they are created. Once a file is created it may only be opened for read, or deleted. Random access is permitted both when reading and writing.

Java's i/o APIs not used directly, but rather all i/o is through this API. This permits things such as:

  • implementation of RAM-based indices;
  • implementation indices stored in a database, via JDBC;
  • implementation of an index as a single file;
Directory locking is implemented by an instance of LockFactory, and can be changed for each Directory instance using setLockFactory(org.apache.lucene.store.LockFactory).

  • Constructor Details

    • Directory

      public Directory()

  • Method Details

    • listAll

      public abstract String[] listAll() throws IOException
      Returns an array of strings, one for each file in the directory.
      Throws:
      NoSuchDirectoryException - if the directory is not prepared for any write operations (such as createOutput(String, IOContext)).
      IOException - in case of other IO errors

    • fileExists

      public abstract boolean fileExists(String name) throws IOException
      Returns true iff a file with the given name exists.
      Throws:
      IOException

    • deleteFile

      public abstract void deleteFile(String name) throws IOException
      Removes an existing file in the directory.
      Throws:
      IOException

    • fileLength

      public abstract long fileLength(String name) throws IOException
      Returns the length of a file in the directory. This method follows the following contract:
      • Must throw FileNotFoundException if the file does not exist (not java.nio.file.NoSuchFileException of Java 7).
      • Returns a value ≥0 if the file exists, which specifies its length.
      Parameters:
      name - the name of the file for which to return the length.
      Throws:
      IOException - if there was an IO error while retrieving the file's length.

    • createOutput

      public abstract IndexOutput createOutput(String name, IOContext context) throws IOException
      Creates a new, empty file in the directory with the given name. Returns a stream writing this file.
      Throws:
      IOException

    • sync

      public abstract void sync(Collection<String> names) throws IOException
      Ensure that any writes to these files are moved to stable storage. Lucene uses this to properly commit changes to the index, to prevent a machine/OS crash from corrupting the index.

      NOTE: Clients may call this method for same files over and over again, so some impls might optimize for that. For other impls the operation can be a noop, for various reasons.
      Throws:
      IOException

    • openInput

      public abstract IndexInput openInput(String name, IOContext context) throws IOException
      Returns a stream reading an existing file, with the specified read buffer size. The particular Directory implementation may ignore the buffer size. Currently the only Directory implementations that respect this parameter are FSDirectory and CompoundFileDirectory.
    • Must throw FileNotFoundException if the file does not exist (not java.nio.file.NoSuchFileException of Java 7).
      • Throws:
      IOException

    • makeLock

      public abstract Lock makeLock(String name)
      Construct a Lock.
      Parameters:
      name - the name of the lock file

    • clearLock

      public abstract void clearLock(String name) throws IOException
      Attempt to clear (forcefully unlock and remove) the specified lock. Only call this at a time when you are certain this lock is no longer in use.
      Parameters:
      name - name of the lock to be cleared.
      Throws:
      IOException

    • close

      public abstract void close() throws IOException
      Closes the store.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Throws:
      IOException

    • setLockFactory

      public abstract void setLockFactory(LockFactory lockFactory) throws IOException
      Set the LockFactory that this Directory instance should use for its locking implementation. Each * instance of LockFactory should only be used for one directory (ie, do not share a single instance across multiple Directories).
      Parameters:
      lockFactory - instance of LockFactory.
      Throws:
      IOException

    • getLockFactory

      public abstract LockFactory getLockFactory()
      Get the LockFactory that this Directory instance is using for its locking implementation. Note that this may be null for Directory implementations that provide their own locking implementation.

    • getLockID

      public String getLockID()
      Return a string identifier that uniquely differentiates this Directory instance from other Directory instances. This ID should be the same if two Directory instances (even in different JVMs and/or on different machines) are considered "the same index". This is how locking "scopes" to the right index.

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • copy

      public void copy(Directory to, String src, String dest, IOContext context) throws IOException
      Copies the file src to Directory to under the new file name dest.

      If you want to copy the entire source directory to the destination one, you can do so like this: 

       Directory to; // the directory to copy to
 for (String file : dir.listAll()) {
   dir.copy(to, file, newFile, IOContext.DEFAULT); // newFile can be either file, or a new name
 }

      NOTE: this method does not check whether dest exist and will overwrite it if it does.

      Throws:
      IOException

    • createSlicer

      public Directory.IndexInputSlicer createSlicer(String name, IOContext context) throws IOException
      Creates an Directory.IndexInputSlicer for the given file name. IndexInputSlicer allows other Directory implementations to efficiently open one or more sliced IndexInput instances from a single file handle. The underlying file handle is kept open until the Directory.IndexInputSlicer is closed.
    • Must throw FileNotFoundException if the file does not exist (not java.nio.file.NoSuchFileException of Java 7).
      • Throws:
      IOException - if an IOException occurs